Productivity of hybrid mulberry on salted soils

. The demand for natural fibers such as silk, wool, and cotton is growing globally, especially for silk fabrics and raw materials from cocoons. In nations with well-established sericulture, efforts are concentrated on enhancing the quantity and quality of cocoon production by growing high-nutrition-value mulberry varieties through asexual reproduction. The study aimed to determine the productivity of the mulberry hybrids during double operation, which required two years of rearing. The silkworm hybrid Ipakchi 1 x Ipakchi 2 was used for the study, and the hygrothermal regime was observed during rearing. the viability of caterpillars varied between 84.8% to 94.43% depending on the feeding option. The use of Karshi-1 x Pionersky hybrid leaves for feeding resulted in the highest viability of 94.43%, compared to 91.08% in the control. However, the lowest viability of 84.8% was observed in the Katlam x Pionersky hybrid. The mass of live cocoons of all tested hybrids was similar, ranging from 2.04-2.21 g.


Introduction
The global demand for natural fibers such as cotton, wool, and silk has been increasing each year, particularly for cocoon raw materials and silk fabrics. In countries with developed sericulture, the focus is on improving the volume and quality of cocoon production by cultivating high-nutritional-value mulberry varieties through vegetative propagation [1,2]. China, India, Vietnam, Thailand, and Uzbekistan are the leading producers of silk thread according to the International Sericulture Commission (INSERCO). There is a growing concern worldwide to improve the biological, productive, and technological properties of silkworms by creating new varieties of mulberry with high nutritional properties [3].
Recent innovations in technology have been used by scientists and breeders worldwide to grow mulberry varieties that are adapted to continental climate conditions, nutritious in terms of chemical composition, and have high water-holding capacity. In developed mulberry growing countries, new agricultural technologies are being developed for the reproduction of highly nutritious mulberry varieties and their use in producing high-quality live cocoons and cocoon thread [4,5]. Research is currently focused on reviving the growth of silkworms, ensuring high levels of cocoon morpho-biological and productive properties, and improving the technological properties of silk fiber.
In our country, important measures are being taken to develop the mulberry and sericulture industries, including the cultivation of high-yielding varietal mulberry seedlings, an increase in the number of harvested cocoons, and the development of new promising breeds and hybrids of the silkworm [6,7]. The systematic laying of new mulberry plantations, renewal of old plantations, and the development of regional programs for the organized season for growing cocoons are seen as essential tasks [8][9][10]. Additionally, scientific research is being conducted to assess the effect of highly nutritious mulberry varieties on cocoon-productive and technological indicators of the silkworm, including the environmental factors affecting the growth of mulberry varieties, reproduction of varietal seedlings, and the survival and development of the silkworm.

Materials and methods
The productivity of silkworm cocoons is determined by the quality of the mulberry leaves they consume. The nutritional value of mulberry leaves is evaluated using biological and chemical methods. The biological method, which involves feeding silkworm caterpillars with the leaves, is considered the most important. In a study, five mulberry hybrids were tested over two years by feeding silkworm caterpillars with their leaves in the spring and autumn. The study found that the nutritional value of the leaves varied depending on the hybrid and the season. The moisture content of the leaves was also found to be important for the silkworms. The study aimed to determine the productivity of the mulberry hybrids during double operation, which required two years of rearing. The silkworm hybrid Ipakchi 1 x Ipakchi 2 was used for the study, and the hygrothermal regime was observed during rearing.
The spring feeding involved rearing the silkworm caterpillars from April 15, 2021, to April 17, 2022, in individual houses of farm workers in Karshi district, while the autumn feeding took place from August 30 of both years. The leaves used for feeding were taken from the entire branch in the spring and from the upper 1/3 of the length of the shoot that had grown back after spring exploitation in the autumn. The study concluded that the nutritional value of the mulberry leaves is crucial for the productivity of silkworm cocoons. Therefore, the quality of the feed, especially the nutritional value and moisture content of the leaves, should be carefully evaluated to obtain high yields of silkworm cocoons.

Results and discussion
On the second day of the second age, a study was conducted with experimental variants consisting of three repetitions of 200 caterpillars, as well as a reserve repetition of 200 caterpillars. During subsequent instars, the health and survival of the caterpillars were monitored through periodic assessments, and any lost or dead caterpillars were replaced from the reserve and taken into account in the overall viability calculations. Leaf harvesting was carried out twice a day based on a standard feeding rate of 900 kg of leaves per box of caterpillars for the entire feeding period. The effects of feeding the caterpillars with the spring leaves of various mulberry hybrids were analyzed, and the results are presented in Table 1, which indicate that the biological characteristics of the caterpillars were not significantly affected by the feeding of the studied mulberry hybrids. During two years of rearing, the development of caterpillars was smooth, and their developmental period ranged from 24.0 to 25.0 days, with a difference of only 0.5 days between the hybrids tested and the control. Viability of caterpillars, a key biological indicator affecting cocoon yield, varied from 84.8 to 94.43% among feeding variants, with a slightly higher viability observed when feeding with the leaf of the mulberry hybrid Karshi-1 x Pionersky ( Table 1). The tested hybrids produced cocoons with similar weights ranging from 2.04 to 2.21 g, and the mass of silk shells was almost identical to cocoon weight. Percentage of silk sheath varied slightly among the hybrids, with the highest percentage observed in the variant of leaf feeding of the Katlama x Pionersky hybrid. Caterpillars fed on the leaf of the control hybrid yielded the highest yield of 85.4 kg per box, while the hybrids Karshi-1 x Pioneer and Winter-hardy x Pioneer produced a yield of 84.3 and 84.0 kg, respectively. The lowest yield was recorded in the variant of feeding with leaves of the hybrid Katlam x Pionersky.
The viability of caterpillars is a crucial factor that affects the yield of cocoons. Based on Table 1, the viability of caterpillars varied between 84.8% to 94.43% depending on the feeding option. The use of Karshi-1 x Pionersky hybrid leaves for feeding resulted in the highest viability of 94.43%, compared to 91.08% in the control. The Winter-hardy x Pionersky and Katlama x SANIISH-14 hybrids produced caterpillars with similar viability as the control at 90.53% and 90.18%, respectively. However, the lowest viability of 84.8% was observed in the Katlam x Pionersky hybrid. The mass of live cocoons of all tested hybrids was similar, ranging from 2.04-2.21 g. The weight of the silk shells almost agreed with the mass of the cocoon, except for the control variant and the leaf feeding variant of the Katlam x SANIISH-14 hybrid, which had the heaviest shell. The percentage of silk sheath varied slightly among the hybrids, with the Katlama x Pionersky hybrid having the highest percentage of silk coat at 21.41%, followed by Katlama x SANIISH-14 (21.29%), Karshi-1 x Pionersky (21.03%), and the control and Winter-hardy x Pioneer hybrids, which had similar percentages at 20.65% and 20.56%, respectively. There was no statistically significant difference between the variants.
Assessing the nutritional value of different mulberry hybrids can be determined by analyzing the technological properties of their silk cocoons. Our study examined the relationship between the quality of mulberry leaves and the yield of cocoons, as well as the effect of nutritional value on the technological properties of cocoons. Results showed that the duration of the caterpillar period was similar across feeding variants, with a difference of only 0.5 days in hybrids compared to the control ( Table 2). The weight of live cocoons and their silk shells was similar across all hybrids, with the heaviest shells found in the control variant and the leaf-feeding variant of the Katlam x SANIISH-14 hybrid. The percentage of silk sheath was also similar across all hybrids, with slightly higher values observed in the variant of leaf feeding of the Katlama x Pionersky hybrid.
The yield of cocoons from one box of grena was closely related to the viability of caterpillars and the weight of the cocoon. The highest yield was obtained when feeding caterpillars with the leaf of the control hybrid, followed closely by the hybrids Karshi-1 x Pioneer and Winter-hardy x Pioneer. The lowest yield was recorded in the variant of feeding with leaves of the hybrid Katlam x Pionersky. Technological analysis of the experimental cocoons revealed that the best coefficient of yield of dry cocoons from raw ones was obtained by feeding caterpillars with leaves of the Karshi-1 x Pioneer and Katlama x Pioneer hybrids (Table 3). These hybrids also produced the highest yields of silk, while the control variant had the lowest silk yield and unwinding. However, it was observed that the variants with the highest percentage of silk yield gave lower values of the metric number of the cocoon thread. Overall, our findings suggest that mulberry can be grown on moderately saline lands in the Karshi steppe, at least for spring feeding, without impairing the fodder (nutritional) properties of its leaves. The results also indicate the potential for creating a large food base under such conditions, as we observed a satisfactory yield of cocoons with normal technological properties across all feeding variants.
The method of rearing and data collection was the same as in spring, the only difference was that the leaf for caterpillar food was collected from the cut upper parts of the shoots that had grown after spring exploitation (1/3 of their length). Table 4 shows data on biological indicators obtained during autumn rearing. The mulberry hybrid Karshi-1 x Pionersky occupies the first place (91.5%) in terms of the viability of caterpillars fed on its leaves. The second place is occupied by Katlama x Pionersky with 85.7% caterpillar viability. The significance of the difference is 0.990, that is, the difference is significant. The remaining mulberry hybrids gave even lower viability values for caterpillars, and for the Katlama x SANIISH-14 and SANIISH-15 x Pionersky hybrids, the obtained viability values are questionable in their accuracy. So, for the first of these hybrids, the error of the mean is 4.1, which means the value of P=more than 5, and for the second hybrid P=3.7, which also indicates the insufficient accuracy of the data obtained (Table 3).
At the same time, the viability index for all hybrids was lower than in spring, only when the Katlama x Pionersky hybrid was fed with a leaf, the viability was equivalent. It should be noted that in the autumn rearing, due to the lack of a special worm farm, it was difficult to maintain the temperature and humidity at the level of requirements, which also affected the duration of the caterpillar period. In terms of hybrids, it was longer than in spring by 11.5 days.From the data of Table 4 it follows that in autumn the cocoons of all variants had a weight close to each other of 1.38-1.45 g, the mass of the shell varied from 305 to 324 mg and the percentage of the silk shell was in the range of 22.12-22.84% (Table 4). Table 5 shows the yield of cocoons from both one gram of caterpillars and one box. On autumn feeding when feeding with a leaf from 1/3 of the length of the shoot, the highest yield from one box of grena (58.67 kg) Table 5. Influence of feed quality on the yield of cocoons Ipakchi 1 x Ipakchi 2 during autumn rearing (average data for 2 years). The leaf-feeding variant of the Karshi-1 x Pionersky hybrid had the highest caterpillar viability and average weight of one living cocoon during the autumn rearing period, resulting in a yield of 54.26 kg, which was higher than the control hybrid. However, in the spring, none of the hybrids produced more cocoons than the control (Table 6). Technological analysis of the autumn-reared cocoons showed a decrease in silk yield and cocoon thread length compared to spring-reared cocoons. The percentage of silk yield ranged from 36.32-38.39%, with the highest yield obtained from the leaf-feeding variant of the Karshi-1 x Pioneer hybrid. Notably, leaf-feeding all hybrids resulted in similar outcomes. The study found that autumn rearing produced cocoons with a thinner cocoon thread and better unwinding, but with smaller continuously unwound thread length and total production length compared to spring rearing. In terms of leaf yield and cocoon yield, the Karshi-1 x Pioneer hybrid was found to be the most productive and salt-tolerant, yielding the highest number of cocoons per 1 centner of leaf and the lowest leaf consumption per 1 kg of cocoons. It also outperformed the control on yield of sheet, cocoons, and raw silk. The study highlights the need for further research on the organization of repeated feeding during the growing season and the operation technique. Overall, the study demonstrates the viability of multiple rearing and obtaining a high yield of cocoons in the newly developed areas of the south (Table 7). Additionally, the autumn rearing resulted in cocoons with a thinner cocoon thread but better unwinding compared to spring rearing. However, the length of the continuously unwound thread and total production length of the thread were smaller during the autumn worm-feeding period. Comparing the productivity of mulberry hybrids in terms of leaf yield and cocoon yield, it should be noted that during the spring season, the yield of cocoons per 1 centner of leaf for four hybrids was at the same level, except for the Katlam x Pionersky hybrid which yielded significantly lower than the other hybrids. Conversely, during the autumn season, the most productive hybrid was the Karshi-1 x Pioneer, which yielded the highest amount of cocoons per 1 centner of leaf and consumed the lowest amount of leaf per 1 kg of cocoons. In fact, this hybrid demonstrated the highest yield of cocoons from 1 box of grena during both seasons, exceeding the control by 105.56%. These findings indicate that the Karshi-1 x Pioneer hybrid is the most productive and salt-tolerant, adapted to the conditions of saline soils in the Karshi steppe, surpassing the control in sheet yield during double operation by 12.14%, cocoon yield by 13.01%, and raw silk yield by 24.0%.

Conclusions
Based on these results, it is planned to organize repeated rearing during the exploitation of mulberries for the intensification of sericulture. However, work on the organization of repeated feeding in the conditions of the Karshi steppe has not yet been carried out. Therefore, it is crucial to determine the start of operation of fodder plantations, the number of rearings during the growing season, and the operation technique.
This study aimed to determine the conditions for maintaining the viability of mulberry, increasing the number of leaves, and improving fodder quality during double operation.
The results of this study demonstrated that multiple rearing is possible in the newly developed areas of the south, resulting in a high yield of cocoons.
It was reported that autumn rearing produced cocoons with a thinner cocoon thread and better unwinding, but with smaller continuously unwound thread length and total production length compared to spring rearing.